1. Field of the Invention
The present invention is directed to a switching relay for moving a plunger to a selected state by energizing a drive coil, and more particularly, to a switching relay (latching) that will remain in the chosen state when voltage is removed from the drive coil. In a preferred form, energizing the selected coil will automatically reset any previously selected position of another drive coil to its original position.
2. Description of the Background Art
Various switching devices are known in the art for selectively making and breaking a set of electrical contacts in order to selectively complete a path for electrical flow or break the path of electrical flow. One such switching device is shown in U.S. Pat. No. 5,712,603. In that switching device, a pair of electromagnets are provided above each end of a ferromagnetic rocker arm, with each end of the rocker arm being connected to electrical switching contacts. Each electromagnet is formed by a coil of wire wound around an iron core. The two electromagnets are alternately energized to pivot the rocker arm back and forth so that the rocker arm causes the electrical contacts to engage one another.
In order to maintain a rocker arm in a selected position, various mechanisms have been developed in the art. For example, a selected electromagnet may remain energized to retain the rocker arm in the selected position. Alternatively, an overcenter magnet arrangement can be utilized to retain the rocker arm in the selected position and the electrical contacts in engagement with one another after electrical energy is removed from the electromagnet. In such a case, it is still necessary to provide a second electromagnet in order to pivot the rocker arm in the opposite direction from the second position to the first position in order to return the electrical contacts to their initial state. Accordingly, two electromagnets must be provided for each rocker arm, greatly increasing the size and cost of the switching device. Further, if an additional switch circuit is provided which must be independently operated, the first position must be reset prior to actuating the additional switch circuit. This type of switching is usually accomplished by complex mechanical sensor contacts and/or solid state electronic sensors.
An alternative arrangement which does not require the use of a second electromagnet is shown in U.S. Pat. No. 3,681,719. Therein, a spring is provided to bias the rocker arm, and thus the electrical contacts, to their initial (failsafe) position. In such a case, the electrical energy must be continuously applied to the electromagnet in order to keep the electrical contacts engaged with one another against the biasing force provided by the spring. Such continuous application of electrical energy is wasteful, produces electromagnetic radiation which may interfere with adjacent components, and may lead to premature burnout of the electrical coil.
Another switching arrangement is shown in U.S. Pat. No. 4,652,840. A solenoid having a plunger slidable therein is biased to an initial position by a compression spring. When the solenoid is energized, the plunger move downwardly against the biasing force of the spring. The plunger engages an electrically conductive bar, which is in turn engaged with a pair of spaced-apart contact surfaces, to thereby form an electrical switch (path). However, the solenoid must remain energized in order to keep the conductive bar engaged with the contact surfaces against the biasing force provided by the spring, and is therefore subject to the same shortcomings set forth above.